Sealing resin composition sealing films and use thereof

ABSTRACT

A sealant resin composition comprises 60 to 95 weight percent of ethylene polymer (PE) and 5 to 40 weight percent of 1-butene polymer (PB), wherein a melt flow rate (MFR) ratio between the two polymers (MFR PE /MFR PB ) is not less than 1. A laminated film obtained by extrusion laminating the resin composition as a sealant film layer over a substrate film adheres tightly to other plastic film by heat sealing and gives a low degree of dependence of heat seal strength on temperature in the heat sealing stage. At the same time the laminated film has an easy peel feature, such that it is readily separated from sealed surfaces after heat sealing, and does not develop any phenomenon of resin threading from the sealed surfaces when they are peeled apart. Accordingly the resin composition is suitably used for the food packaging material.

This application is the national phase under 35 U.S.C. § 371 of PCTInternational Application No. PCT/JP01/07116 which has an Internationalfiling date of Aug. 20, 2001, which designated the United States ofAmerica.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a sealant resin composition, a sealantfilm having both heat sealability and an easy peel feature, andlaminated films and containers for which the sealant film is utilized.

BACKGROUND OF THE INVENTION

A sealant film possessing an easy peel feature used for packagingmaterials in the manufacture of containers is required to satisfy both ahermetic seal and the easy peel feature. However, these two propertiesconflict with each other. Out of these two features, the hermetic sealis required to constantly yield a heat seal strength at least sufficientto protect the contents and further show a low degree of dependence of aheat seal strength on temperature so as to be compatible with a widevariety of substrates. On the other hand, with regard to the easy peelfeature, the properties required from a viewpoint of preserving a goodappearance and preventing contamination of the contents include not onlythe ability to leave no peel marks (threaded resinous residue) when thesealed surfaces are peeled apart, but also total inhibition of aphenomenon of resin threading while a heat sealing operation is requiredto be executed to the extent that the sealed surfaces can be readilyseparated by hand. Moreover, odor transfer from the film to foodstuff ispreferably avoided wherever possible in the case of the food packagingsealant film that is offered to the food packaging uses.

So far many types of materials have been developed as a resin for thesealant film. For instance, U.S. Pat. No. 4,189,519 discloses an easypeel sealant material comprising ethylene-vinyl acetate copolymer (EVA)and poly-1-butene. Additionally, U.S. Pat. No. 4,666,778 discloses aneasy peel sealant material comprising an ethylenic resin, poly-1-butene,and polypropylene. Nevertheless, according to studies conducted by theinventor of the present invention, the former is apt to be accompaniedby transfer of acetic acid odor to the contents and the latter does notreadily facilitate adjustment of the seal strength to an adequatedegree.

Japanese Laid-open Patent Application No. 315,443/1989 discloses acomposition for the easy peel sealant use comprising a poly-1-butenehaving an average molecular weight of not less than 500,000 andlow-density polyethylene. The composition is, however, usable only withlimited types of processing techniques due to the high molecular weightof its poly-1-butene content and its low melt flow rate, besides havingnarrow tolerances in terms of controllability of the seal strength.Although the “Research Disclosure” magazine (issue No. 38433) refers toan easy peel laminated body comprising poly-1-butene and polyethylenepolymerized with the metallocene catalyst, this literature fails to giveany description regarding the phenomenon of resin threading.Furthermore, Japanese Laid-open Patent Application No. 337,829/1998describes that a composite film constructed of a seal layer comprised oflow-density polyethylene and poly-1-butene and a substrate layerproduced from polyethylene resin gives good hermetic seal andopenability.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide asealant resin composition which maintains an adequate balance betweenheat sealability and an easy peel feature, and is featured by a lowdegree of dependence of heat seal strength on temperature in a heatsealing stage, and also is hardly susceptible to a phenomenon of resinthreading from sealed surfaces when they are peeled apart.

It is another object of the invention to provide a sealant film formedfrom the composition and laminated films and containers for which suchsealant film is utilized.

Namely, the present invention relates to a sealant resin compositioncomprising compositional units derived from ethylene and compositionalunits derived from 1-butene, wherein the composition has a melt flowrate of 0.2 to 30 g/10 min., and a film formed from the composition hasa heat seal strength of 1 to 10 N/15 mm. when the film is heat sealed at150° C. and does not substantially produce any thread-like resinousresidue when the heat sealed surfaces are peeled apart.

The sealant resin composition is preferably a resin compositioncomprising an ethylene polymer having a melting point in a region of 100to 125° C. as measured by a differential scanning calorimeter (DSC) anda 1-butene polymer having a melting point in a region of 70 to 130° C.as measured by the same method. The resin composition has preferably twoor more melting peaks in a region of 70 to 130° C. as observed in theDSC test and more preferably has a melting peak having a largest peakarea among them in a region of 100 to 125° C. Further the resincomposition has preferably a microstructure constituting anislands-in-the-sea structure.

Furthermore, the invention relates to a sealant resin compositioncomprising 60 to 95 weight percent of an ethylene polymer having a meltflow rate of 0.2 to 30 g/10 min. and a density of 0.900 to 0.940 g/cm³and 5 to 40 weight percent of a 1-butene polymer having a melt flow rateof 0.1 to 25 g/10 min. and a 1-butene unit content of 60 to 100 mol.percent, wherein a ratio of the melt flow rate (MFR_(PE)) of ethylenepolymer to the melt flow rate (MFR_(PB)) of the 1-butene polymer, i.e.,MFR_(PE)/MFR_(PB), is not less than 1. The preferred density of the1-butene polymer is within a range of 0.880 to 0.925 g/cm³.

The ethylene polymer may be either ethylene homopolymer orethylene-α-olefin copolymer, although high-pressure process low-densitypolyethylene, linear ethylene-α-olefin copolymer and a compositionthereof are particularly preferred. And, the 1-butene polymer may beeither 1-butene homopolymer or 1-butene-α-olefin copolymer. This resincomposition is suited to the film forming and is capable of providingfilms possessing both the easy peel feature and the heat sealability.

The present invention, furthermore, relates to a sealant film formedfrom the sealant resin composition having a thickness of 3 to 100 μm andeasy peel feature, which can be manufactured in the extrusion laminationprocess, cast molding or tubular film process. It is an unique featureof this film that even when the sealed surfaces produced by lap jointingits surfaces together or lap jointing its surface to a film of anotherkind are peeled apart, there is not substantially observed anyphenomenon of resin threading from the peeled surfaces.

The invention, moreover, relates to a laminated film comprising a layerof the sealant film and at least a layer of a film selected from thegroup consisting of polyolefin film, polystyrene film, polyester film,polyamide film, a laminated film constructed of polyolefin film and gasbarrier resin film, aluminum foil and deposited film, which is suitablefor a packaging film having both the heat sealability and the easy peelfeature.

There can be cited as an embodiment an integrated laminated filmobtained by laminating in the following order a layer of the sealantfilm, a layer of polyolefin film and at least a layer of a film selectedfrom the group consisting of polystyrene film, polyester film, polyamidefilm, laminated film comprised of a polyolefin film and gas barrierresin film, aluminum foil and deposited film.

The invention, furthermore, relates to containers capable ofhermetically sealed packaging a content by way of making two oppositesurfaces of the sealant film layer of the laminated film to be lapjointed to each other by heat sealing or by way of lap jointing thesealant film layer of the laminated film to a molding produced from aresin of another kind by heat sealing. In cases where the content isfoodstuff, odor hardly transfers from this container to the containedfoodstuff.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a sealant resin composition comprisedof compositional units derived from ethylene and compositional unitsderived from 1-butene, and a sealant film, laminated films andcontainers for which the composition is utilized. The invention and itscomposing elements are explained in detail as follows.

Sealant Resin Composition (1)

The sealant resin composition (1) of the present invention has suchchemical structure that at least compositional units derived fromethylene and compositional units derived from 1-butene are containedtherein. It is a so-called olefinic resin. Since both of thesecompositional units exist therein, this resin composition possesses bothheat sealability and the easy peel feature.

The compositional units each can be detected by infrared absorptionspectrum analysis. That is to say, compression molded film specimens ofthis resin composition are subjected to infrared absorption spectrumanalysis, whereby identification of the two compositional units can beexecuted in light of a finding that the absorption of the compositionalunit derived from ethylene occurs in a region of 700 to 740 cm⁻¹ and theabsorption of the compositional unit derived from 1-butene occurs in aregion of 750 to 780 cm⁻¹.

More specifically, it is desirable that this resin composition comprisesat least an ethylene polymer having a melting point in a region of 100to 125° C. as measured by a differential scanning calorimeter (DSC) anda 1-butene polymer having a melting point in a region of 70 to 130 CC asmeasured by the same method. The DSC test is tollowed through by heatingthe specimen of this resin composition from room temperature to 200° C.to completely melt it and maintaining the temperature for 10 min. andafter the lapse of this dwell time it is cooled to 0° C. at a coolingrate of 10° C. /min. Once again, heating is resumed and heating iscarried out at a heating rate of 10° C./min., and observation is madethroughout this cycle to record resultant endothermic peaks. Thepositions of endothermic peak thus emerged are recorded as the meltingpoints of the sample polymers.

It is preferable that the resin composition has two or more meltingpeaks on the DSC thermal curve in a region of 70 to 130° C., and themelting peak having a largest peak area exists in a region of 100 to125° C. When the melting peak having the largest peak area exists in theregion, a sealant film formed from the resin composition possesses goodlow temperature heat sealability and does not substantially produce anyphenomenon of resin threading when the sealed surfaces are peeled apart.

In the measurement of melting points by the DSC, in cases where meltingpeaks attributed to the components of the resin composition are observedin a separated state, a peak found to have a larger peak area by overallcomparison may be treated as the melting peak having a largest peakarea. On the other hand, in cases where an endothermic peak is notseparated but forms a shoulder of another peak, the peak that does notassume the shape of the shoulder is to be treated as the melting peakhaving a largest peak area. In other cases where endothermic peaks arenot completely separated, but are observed to assume a double-peakshape, the product of the peak height and the width at half-height ofthe endothermic peak is calculated for each peak and the peak having alargest value is treated as the melting peak having a largest peak area.

It is desirable that this resin composition is constituted with amicrostructure wherein resins derived from at least two species ofcompositional units form so-called an “islands-in-the-sea structure ”.More preferably, the ethylene polymer and the 1-butene polymer maymutually have the appearances of the islands-in-the-sea structure.Furthermore preferably, the islands-in-the-sea structure assumes theform of the body of water built by the ethylene polymer wherein the1-butene polymer is dispersed all over as if islands in it. It isinferred that the islands-in-the-sea structure of the resin compositioncontributes to the generation of an adequate balance between the heatsealability and the easy peel feature.

The microstructure of the resin composition can be verified by atransmission electron microscope (TEM) examination which is performed bypreparing in the first place thin slices from a sample of the resincomposition available in the pellet or film form using a microtome,etc., and then, after dyeing those slices with osmium, examining thespecimen under the TEM of 10,000 magnifications.

On the other hand, it is desirable that this resin composition has amelt flow rate of 0.2 to 30 g/10 min. as measured in accordance withASTM D-1238 under conditions of 190° C. and a load of 2.16 kg,preferably 1 to 25 g/10 min., more preferably 2 to 25 g/10 min., andfurthermore preferably in excess of 2 g/10 min., but not more than 25g/10 min. So long as the melt flow rate remains within these ranges, theresin composition yields good film moldability and eventually asufficient mechanical strength is secured when converted into a filmlayer

The heat seal strength of film formed from this resin composition whenit is heat sealed at 150° C. is 1 to 10 N/15 mm, and preferably 1 to 8N/15 mm. So long as the heat seal strength remains within the ranges,the heat sealed film gives a practically sufficient adhesive strength aswell as good peelability, and thus serves as a favorably workablepackaging material.

It is an important aspect of the present invention that there is notsubstantially produced any fluffing, so-called threading, from thesurface of sealant film layer, when this film is peeled apart from thesealed surface after heat sealing it to an adherend, and hence concernsabout contamination of the packed content may be thus eliminated. Thephenomenon of threading is observed by visual examination.

The sealant resin composition (1) of the present invention is, forexample, manufactured by blending the ethylene polymer with the 1-butenepolymer as described latter.

Sealant Resin Composition (2)

The resin composition (2) of the present invention comprises at leastthe below-mentioned ethylene polymer and 1-butene polymer. That is tosay, it is a resin composition comprising 60 to 95 weight percent of anethylene polymer having a melt flow rate of 0.2 to 30 g/10 min. and adensity of 0.900 to 0.940 g/cm³ and 5 to 40 weight percent of a 1-butenepolymer having a melt flow rate of 0.1 to 25 g/10 min. and a 1-buteneunit content of 60 to 100 mol. percent, wherein the ratio of the meltflow rate (MFR_(PE)) of the ethylene polymer to the melt flow rate(MFR_(PB)) of the 1-butene polymer, i.e., MFR_(PE)/MFR_(PB), is not lessthan 1.

Ethylene polymer:

The ethylene polymer usable for the present invention may be eitherethylene homopolymer or ethylene-α-olefin copolymer. Its molecularstructure may be either of the linear type or of the branched type, thelatter of which having long or short side chains.

In the case of copolymer, α-olefin as a comonomer is an α-olefin havingpreferably 3 to 20 carbon atoms, and more preferably 3 to 10 carbonatoms, and is random copolymerized with ethylene. There can be cited asspecific examples of such α-olefin the following: Propylene, 1-butene,1-pentene, 1-hexene, 1-heptene, 1 -octene, 1-decene, 1-undecene,3-methly-1-butene, 3-methyl-1-pentene, 4-methyl-1-pentene,4-methyl-1-hexene, 4,4-dimethyl-1-hexene and any combination thereof.Insofar as required, it may contain a small amount of othercomonomer(s). It is desirable that the ethylene content of the copolymeris 85 to 99.9 mol. percent, and preferably 90 to 99.5 mol. percent. Thedesirable α-olefin content is 0.1 to 15 mol. percent and preferably 0.5to 10 mol. percent.

The density of the ethylene polymer is 0.900 to 0.940 g/cm³, andpreferably 0.905 to 0.930 g/cm³. Such ethylene polymer falls under thecategory of low-density polyethylene or medium-density polyethylene. Theethylene polymer falling in this density range possesses alow-temperature heat sealability, and an obtained container can befilled with a content at a high filling speed, when the container isfinally fabricated from the film, since the surface of the inner layerfilm (the sealant layer) possesses a low tackiness. Thereupon, thedensity of the ethylene polymer is measured using a density gradienttube by way of subjecting the strand obtained in the below-mentionedmelt flow rate measurement to a 1 hr-long heat treatment at atemperature of 120° C. and then allowing it to cool down to roomtemperature after 1 hr.

The melt flow rate (MFR) which is measured in accordance with ASTMD-1238 under the conditions of 190° C. and a load of 2.16 kg is 0.2 to30 g/10 min., preferably 1.0 to 25 g/10 min., and more preferably 2.0 to25 g/10 min. So long as the melt flow rate remains within these ranges,the ethylene polymer may be formed into a film at a high molding speedusing a conventional molding machine. It is desirable that the meltingpoint measured by the DSC test stands in a region of 100 to 125° C.

The ethylene polymer whose properties such as density, melt flow rate,and melting point are within the ranges may be manufactured throughhomopolymerization of ethylene or copolymerization of ethylene withα-olefin using a radical polymerization catalyst, Phillips catalyst,Ziegler-Natta catalyst or metallocene catalyst.

In particular, the preferred type is so-called high-pressure processlow-density polyethylene produced in a tubular-type reactor or anautoclave-type reactor using a radical polymerization catalyst. Aboveall, the polymer whose melt flow rate (MFR) as related to melt tension(MT) (as measured at 190° C.; unit: mN) satisfies the following equationis preferred from the viewpoint of controlling conditions of the filmforming:40×(MFR)^(−0.67)≦MT≦250×(MFR)^(−0.67)

Linear ethylene-α-olefin copolymer manufactured with Ziegler-Nattacatalyst or metallocene catalyst also may be favorably employed. Sincelong chain or short chain branches may be generated by adjusting thepolymerization conditions, ethylene-α-olefin copolymer thus producedalso may be used.

Furthermore, this ethylene polymer may be used in the form of acomposition prepared as a blend with ethylene polymer of severaldifferent kinds. For instance, when a composition of high-pressureprocess low-density polyethylene and linear ethylene-α-olefin copolymeris prepared in conformance with a [(High-pressure process low-densitypolyethylene) to (Linear ethylene-α-olefin copolymer)] mixing ratiowhich is within a range of 0/100 to 75/25 (parts by weight), andpreferably 5/95 to 75/25 (parts by weight), the balance between the sealstrength and the peel strength may be readily adjusted.

That is to say, in light of the decline in the seal strength which tendsto result from an increased mixing ratio of the high-pressure processlow-density polyethylene, the balance between the seal strength and thepeel strength may be adjusted to a desired degree by way of increasingthe relative content of high-pressure process low-density polyethylenefor such application areas that particularly require the easy peelfeature, and, conversely, by way of increasing the relative content oflinear ethylene-α-olefin copolymer for such application areas where ahigh seal strength is necessitated.

1-Butene Polymer:

1-Butene polymer usable for the present invention is 1-butenehomopolymer or a copolymer of 1-butene with α-olefin of any kind having2 to 20 carbon atoms, and preferably 2 to 10 carbon atoms except1-butene. As specific examples of such α-olefin, there can be cited thesame α-olefins as described before. Above all, ethylene, propylene,1-hexene, 4-methyl-1-pentene, and 1-octene are preferred. A small amountof other type of comonomer(s) may be contained therein insofar asrequired. It is desirable that a 1-butene content of the copolymer is 60to 100 mol. percent, and preferably 70 to 100 mol. percent, and anα-olefin content is 0 to 40 mol. percent and preferably 0 to 30 mol.percent.

The density of the 1-butene polymer is preferably 0.880 to 0.925 g/cm³,and more preferably 0.885 to 0.920 g/cm³. Since the surface of the filmobtained from the resin composition possesses a low tackiness when thedensity of the 1-butene polymer falls in this range, a containerobtained from the film may be filled with the content at a high fillingspeed in the final packaging stage.

The melt flow rate (MFR) which is determined in accordance with ASTMD-1238 under conditions of 190° C. and a load of 2.16 kg is 0.1 to 25g/10 min., preferably 1.0 to 25 g/10 min., more preferably 2 to 25 g/10min., furthermore preferably in excess of 2 g/10 min., but not more than25 g/10 min., and most preferably 2.5 to 25 g/10 min.

So long as the melt flow rate of 1-butene polymer remains within theranges, the resin composition does not exert an excess load onto themotor in the molding machine, and hence the film may be formed under alow resin pressure. Even if the condition of increased film formingspeed is adopted, the emission of odor (fume) in consequence ofoxidative degradation of the resin composition or the blocking of filmmay be restrained, since the heat developed by shear stress is held to alow degree. When the melt flow rate of 1-butene polymer is decreased,surging (the phenomenon wherein the extrudate becomes inconsistent)tends to take place in the film forming stage with the result that thethickness of film becomes inconsistent and/or the draw-downcharacteristics is deteriorated. However, such a situation may scarcelyoccur when the melt flow rate of 1-butene polymer is within said ranges.Furthermore, it becomes easy to adjust the heat seal strength and lowerthe degree of dependence of the heat seal strength on heat sealtemperature.

It is desirable that the melting point as measured by the DSC fallswithin a region of 70 to 130° C.

Such 1-butene polymer can be manufactured through a polymerizationprocess with a stereoregular polymerization catalyst disclosed inJapanese Patent Publication No. 7088/1989, and Japanese Laid-open PatentApplication Nos. 206415/1984, 206416/1984, 218507/1992, 218508/1992,225605/1996, etc., respectively. For the purpose of the presentinvention, either type of the 1-butene polymers described before may beemployed or any combination of two or more types may be employed.

Resin composition:

The resin composition (2) of the present invention comprises at leastthe ethylene polymer and the 1-butene polymer described before, and thedesirable mixing ratios are 60 to 95 weight percent, and preferably 65to 85 weight percent for the ethylene polymer and 5 to 40 weightpercent, and preferably 15 to 35 weight percent for the 1-butenepolymer, wherein the sum of the two polymers is 100 weight percent.Insofar as the two polymers remain within the ranges, the film formedfrom the composition gives an adequate balance between the heatsealability and the easy peel feature, and hence easy openability may beprovided in favor of the users, while a practical heat seal strengthrequired for the packaging material may be secured at the same time.Consequently, this resin composition is suitably usable formanufacturing a sealant film having the easy peel feature.

Furthermore, it is desirable that the ratio of the melt flow rate of theethylene polymer (MFR_(PE)) to that of the 1-butene polymer (MFR_(PB))constituting this resin composition, i.e., (MFR_(PE)/MFR_(PB)), is notless than 1. More specifically, the (MFR_(PE)/MFR_(PB)) ratio isrepresented by the following equations.That is to say, 1≦MFR _(PE) /MFR _(PB),preferably 1≦MFR _(PE) /MFR _(PB)≦20,and more preferably 1≦MFR _(PE) /MFR _(PB)≦10.So long as the melt flow ratio between the two polymers satisfies theabove relationship, such otherwise resultant phenomenon of resinthreading from the peeled surfaces may be substantially prevented whenthe heat sealed films are separated at the interface.

That is to say, when the sealant film formed from this resin compositionis bonded to an identical film by heat sealing or the sealant film isbonded to a film formed from polyethylene, ethylene-vinyl acetatecopolymer, polypropylene, etc. by heat sealing and the sealant film isforcibly peeled apart, there does not substantially occur any phenomenonof resin threading from the peeled surfaces.

It is preferable that this resin composition has such structure that theethylene polymer constitutes the matrix phase and 1-butene polymerconstitutes the dispersant phase contained therein in the state ofmicro-dispersion, that is to say, both of which creating the aforesaidislands-in-the-sea structure. By virtue of the melt viscosity of the1-butene polymer controlled to within the aforesaid specific range inrelation to the melt viscosity of the ethylene polymer, the dispersed1-butene polymer assumes the spherical shape. It is inferred that suchislands-in-the-sea structure of the resin composition contributes to theprevention of the phenomenon of resin threading from the peeled surfaceswhen sealed films are peeled apart. Furthermore, it is desirable thatthe resin composition of the present invention possesses at the sametime the properties of the resin composition (1).

Such additives as antioxidant, heat stabilizer, antiweatheringstabilizer, slip agent, antiblocking agent may be added to the resincomposition insofar as required to the extent not deviating from theobject of the present invention. The nucleating agent disclosed in U.S.Pat. Nos. 4,320,209, 4321334, and 4322503, respectively, may be alsoadded.

In the manufacture of the resin composition, specific amounts ofethylene polymer, 1-butene polymer and, insofar as required, variousadditives may be homogeneously mixed and are, insofar as necessary,kneaded. Mixing may be accomplished utilizing Henschel mixer, Banburymixer, tumbler mixer, single-screw or twine-screw extruder, etc.

The resin composition explained so far can be used as a resin forproducing film by extrusion lamination, cast molding, or tubular filmprocess, since it has good processibility. In particular, it is suitablefor extrusion lamination.

Sealant Film

By way of forming film from the resin composition, sealant film can bemanufactured as a packaging material requiring the easy peel feature.The process to employ for forming a film may be either cast molding ortubular film process. Film having uniform thickness and good appearancemay be produced at a high forming speed usually at a resin temperatureof 180 to 240° C. As for the film thickness, 3 to 100 μm is adequate forthe sealant layer. A sealant film layer can be also formed by extrusionlaminating the resin composition directly onto a substrate film inaccordance with a procedure described later.

When a stack of two layers of this sealant film is heat sealed togetheror this sealant film placed over a film of another kind is heat sealed,the lap jointed two layers and yet the two layers may be separated fromeach other with an adequate force. Therefore the obtained film may beutilized as a film possessing both the heat sealability and the easypeel feature. Besides, there is hardly produced any thread-like resinousresidue on the peeled surfaces when the jointed films are forciblypeeled apart.

There is no particular limitation to the conditions of heat sealing.When heat sealing is executed under conditions of a sealing temperatureof 120 to 180° C. and a sealing pressure of 0.1 to 0.5 MPa, practicallysufficient adhesive strength may be achieved and inconsistency in theadhesive strength due to variances in the heat sealing temperature isminimized. For example, the adhesive strength remains in a range of 1 to10 N/15 mm when the heat sealing is executed under conditions of theheat sealing temperature of 150° C., the sealing pressure of 0.2 MPa andthe sealing time of 1 sec.

Laminated Film

While this sealant film is, as a matter of course, usable by itself, itis often offered to the packaging film or sheet uses in the form oflaminated film in which this sealant film is laminated over a substratefilm. The sealant film is also usable as a material for containers orcontainer covering material.

There is no particular limitation to the usable type of substrate film.In light of the intended serviceability as a packaging material,appropriate types are selected from among the following films. Namely,polyolefin film produced from polyethylene, polypropylene, etc.; filmproduced from styrene resin; polyester film produced from polyethyleneterephthalate, polybutylene terephthalate, etc.; polyamide film producedfrom Nylon 6, Nylon 66, etc.; laminated film constructed of polyolefinfilm and gas barrier resin film produced from such as polyamide resin orethylene-vinyl alcohol copolymer resin; metal foil produced fromaluminum, etc.; film deposited with aluminum, silica, etc. Among thosevarious films, the usable type is not limited to one type, but two ormore types may be used in combination.

Since the sealant film layer is to constitute at least one outermostlayer in the laminated film, either one of the following processes maybe adopted for manufacturing the laminated film. Namely, the extrusionlamination accomplished by laminating the resin composition explainedabove directly or indirectly onto a substrate film; the dry laminationof the sealant film over a substrate film; and the co-extrusionaccomplished by extruding resins to constitute the two layers.

The laminated film is basically constructed of a sealant film and asubstrate film. However, in cases where the adhesive strength betweenthe sealant film and the substrate film is insufficient, there may beadopted modified combinations of films. For example, it may well be alamination constructed of at least triple layers fabricated by stackinga sealant film layer, a film layer of a different type havingadhesivity, and a substrate film in said order. The sealant film may beemployed in combination with any appropriate films in light of theintended serviceability of the required packaging material.

As an embodiment for the laminated film, there can be cited a filmconstructed of a sealant film layer, a polyolefin film layer and a filmlayer of another material. As the film layer of another material, therecan be cited a layer selected from the aforementioned group consistingof polystyrene film; polyester film; polyamide film; laminated filmconstructed of polyolefin film and gas barrier resin film; aluminumfoil; and deposited film.

In cases where the polyolefin film layer cannot be bonded to the filmlayer of another material to have sufficient adhesive strength, thelamination may be constructed of a sealant film layer, a polyolefin filmlayer, an adhesive layer, and a film layer of another material. When ananchor coating agent such as a urethane-based adhesive or anisocyanate-based adhesive, or modified polyolefin such as unsaturatedcarboxylic acid-grafted polyolefin is used as the adhesive resin of theadhesive layer, the state of firm bond to the neighboring layers may beachieved.

Containers

Sealed containers, for example, pouch-shape containers, can bemanufactured by means of firmly lap jointing two sheets of the laminatedfilm so as to have their sealant film layers face each other, or bendingthe laminated film to let its sealant film layer assume a face-to-faceposition, or making the sealant film layer of the laminated film face afilm of another kind, and then heat sealing from either outer surface ofthe stacked films along their edges so that the obtained article mayconform the configuration of the intended container. Filled packages canbe automatically obtained in case the pouch-shape container fabricationline is integrated with the filling line of content, that is to say, thebottom section and the side sections are heat sealed in the first place,and then after filling the pouch with the content, the top section ofthe package is heat sealed. Accordingly, this laminated film can beutilized as the feed material compatible with the regular automaticpacking machine that is capable of packaging solids such as snack food,etc. and pulverized or liquid materials.

Furthermore, a filled package can be obtained by filling a containermolded into the cup-shape by vacuum forming or deep drawing thelaminated film (or sheet) or film (or sheet) of another kind, orconventional injection-molded container, and then covering suchcontainer with the laminated film or a film of another kind as thecovering material, and finally providing a heat seal from the top of thecontainer or around the circumference of its side. In this case, thesealant film of the present invention can be utilized as the sealantlayer of the covering material, the sealant layer of the container perse, or both of them. The obtained container is suitably utilized forpackaging instant noodle pre-packed in a cup, “miso” bean paste, ham,bacon, jelly, pudding, snack food, etc.

The construction and the manufacturing method of the container is by nomeans limited by the explanation given above, but may be changedliberally. As for the other type of film or container usable with thesealant film or the laminated film of the present invention,conventional packaging materials formed from such resins aspolyethylene, ethylene-vinyl acetate copolymer, and polypropylene may beused. For example, packaging containers can be formed by means ofmolding a container having a flange at its opening portion from suchmaterial and then, after placing a sealant film on the flanged opening,lap jointing the two surfaces, and then heat sealing the stacked layers.Since the sealant film or the sealant film layer may be heat sealed withthe packaging material with a sufficient adhesive strength anddemonstrates the easy peel feature when the seal is opened, thiscontainer can be suitably used as a packaging container that is capableof providing hermetic seal and easy peel feature, in particular in thefood packaging area.

EXAMPLES

The present invention is illustrated in reference to the followingexamples; however, these examples are not to be construed to limit thescope of the present invention.

Firstly, the types of resin used in examples and their properties areshown in Table

TABLE 1 Comono- mer & Poly- MFR Resin Content merization (g/10 Densitycode Kind of Resin (mol. %) catalyst min.) (g/cm³) PE 1 Linearlow-density MP T 2.0 0.920 polyethylene 3 PE 2 Linear low-density H M4.0 0.920 polyethylene 3.5 PE 3 Linear low-density B T 20 0.920polyethylene 3 PE 4 High-pressure process — R 4.0 0.918 low-densitypolyethylene 0 PE 5 High-pressure process — R 10 0.918 low-densitypolyethylene 0 PB 1 1-Butene-ethylene E T 1.0 0.910 copolymer 1 PB 21-Butene polymer — T 2.5 0.915 0 PB 3 1-Butene-ethylene E T 4.0 0.910copolymer 5 PB 4 1-Butene polymer — T 20 0.910 0 LEGEND: Comonomer: “MP”denotes 4-methyl-1-pentene, “H” denotes 1-hexene, “B” denotes 1-butene,and “E” denotes ethylene. Polymerization catalyst used at resinproduction: “T” denotes titanium catalyst, “M” denotes metallocenecatalyst, and “R” denotes radical polymerization catalyst.

Examples 1-9 and Comparative Examples 1-3

Resin compositions for the sealant layer film were prepared using theresins shown in Table 1 which were mixed at the mixing ratios shown inTable 2. In the next step, double layer films were formed using a linearlow-density polyethylene having a density of 0.920 g/cm³ and a melt flowrate of 2.0 g/10 min. as the substrate layer film. The film wasconstructed of a substrate layer having a thickness of 50 μm and asealant layer having a thickness of 20 μm.

For forming the double layer film, an extruder having a screw diameterof 40 mm was used to form the substrate layer and an extruder having ascrew diameter of 30 mm was used to form the sealant layer, and then amulti-layer casting machine equipped with a 30 cm-wide die was used toobtain a double layer films. For each layer, the applied formingtemperature was 220° C., the chill roll temperature 30° C., and the filmtake-up speed 10 m/min.

Results of the DSC tests to determine the melting peaks of theconstituents constituting the resin composition for the sealant layerand the transmission electron microscope (TEM) examination to determinethe presence or absence of phase separation (the islands-in-the-seastructure) are shown in Table 2, respectively.

Moreover, for evaluating properties of the obtained double layer film,tests were performed in accordance with the following testing procedureswith respect to its optical property, heat seal strength and phenomenonof resin threading from the peeled surfaces. Results of these tests areshown in Table 2.

(1) Optical property: Haze was determined in accordance with ASTMD-100361. Pertinent values are indicated by percentage.

(2) Heat seal strength: Two 15 mm-wide oblong specimens were prepared.After stacking them so that one sealant layer faces the other, heatsealing was executed from the substrate film side at a specifiedtemperature under conditions of a load of 0.2 MPa and a sealing time of1 sec. Thereupon, the bonded layers were peeled apart at the interfacein the direction of 180 deg. at a speed of 300 mm/min. The peel strengthwas measured and the obtained value was indicated as the heat sealstrength (N/15 mm width).

(3) Resin threading phenomenon: After the heat seal strength test, thestate of peel on the peeled surfaces was examined by a visual test.

The case in which thread-like resin remained on the peeled surfaces as aresinous residue and an appearance of the peeled surfaces was not sogood was reported as “Yes (Inferior).”

On the contrary, the cases in which there was not found any thread-likeresinous residue and an appearance of the peeled surfaces was good wasreported as “None.”

TABLE 2 Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Compar.Compar. Compar. ple ple ple ple ple ple ple ple ple Example ExampleExample 1 2 3 4 5 6 7 8 9 1 2 3 Resin composition (% by wt.) PE 1 80 70— — — — — — — 100 70 70 PE 2 — — 70 55 40 25 — — — — — — PE 3 — — — — —— 70 70 70 — — — PE 4 — — — 15 30 45 — — — — — — PB 1 20 30 — — — — 30 —— — — — PB 2 — — 30 30 30 30 — 30 — — — — PB 3 — — — — — — — 30 — 30 —PB 4 — — — — — — — — — — 30 MFR_(PE)/MFR_(PB) 2.0 2.0 1.6 1.6 1.6 1.6 208 5 — 0.5 0.1 Melting peak 112 112 120 108 108 108 112 120 104 120 104123 by DSC 120 120 125 120 120 120 120 125 120 120 120 (° C.) 125 125125 Presence of phase Yes Yes Yes Yes Yes Yes Yes Yes Yes None Yes YesSeparation Haze (%) 6.2 8 5.5 8.4 12.7 7.6 54 38 15 2.9 4.5 14.1 Heatseal strength (N/15 mm) Sealing temperature (° C.) 120 3.5 4.9 5.2 2.41.1 1.0 4.0 3.5 3.2 13.1 1.4 2.0 130 7.6 5.3 5.8 3.0 1.5 1.1 6.1 3.8 3.615.0 2.2 2.4 140 8.8 5.9 6.4 3.9 1.9 1.4 9.5 5.4 5.0 15.8 3.5 2.4 1508.6 6.3 6.9 3.7 2.4 1.8 9.6 6.5 6.1 16.4 4.0 2.2 160 8.6 6.4 7.0 4.1 2.82.0 9.4 7.3 7.0 16.8 4.1 2.4 Presence of the None None None None NoneNone None None None None Yes Yes phenomenon of (Inferior) (Inferior)resin threading from the peeled surfaces

As can be seen from Table 2, the heat seal strength was practicallysufficient, but remained in a range of permitting hand peeling by way ofemploying a composition comprised of ethylene polymer and 1-butenepolymer as mentioned in the relevant Examples for the sealant layer, andhence a laminated film having a good balance between the two propertiescould be obtained. Meanwhile, it was learned that there was not observedany phenomenon of resin threading from the peeled surfaces uponseparation of the films, and hence it was found to be a suitablepackaging material. With the Comparative Examples taken intoconsideration, it was learned that the MFR_(PE)/MFR_(PB) values wereclosely related with the occurrence of the phenomenon of resin threadingfrom the peeled surfaces.

Examples 10-12 and Comparative Example 4

A double layer film was formed using a composition prepared by mixing 75weight percent of PE 2 and 25 weight percent of PB 2 as shown in Table 1for the sealant film layer and a linear low-density polyethylene havinga density of 0.920 g/cm³ and a melt flow rate of 2.0 g/10 min. for thesubstrate film layer. The film was constructed of a substrate layerhaving a thickness of 50 μm and a sealant layer having a thickness of 20μm.

An extruder having a screw diameter of 40 mm was used to form thesubstrate layer and an extruder having a screw diameter of 30 mm wasused to form the sealant layer, and then a multi-layer casting machineequipped with a 30 cm-wide die was employed to obtain the double layerfilm. For each layer, the applied forming temperature was 220° C., thechill roll temperature 30° C., and the film take-up speed 10 r/min.

By way of stacking over the sealant layer side of the obtained doublelayer film each adherend film having a thickness of 200 μm as mentionedin Table 3, heat sealing was executed under the same conditions asadopted for the said heat seal strength test, and then the heat sealstrength was measured. At the same time, the peeled surfaces wereobserved so as to evaluate whether the phenomenon of resin threading hadtaken place from the peeled surfaces. Results of the tests are shownalongside in Table 3.

TABLE 3 Example Example Example Compar. 10 11 12 Example 4 Kind ofadherend* LDPE HDPE PP PS Heat seal strength (N/15 mm) Sealingtemperature 120 (° C.) 4.6 4.1 — Failed 130 5.1 4.7 5.6 in sealing 1405.4 5.4 6.3 150 5.8 5.7 6.7 160 5.9 6.0 7.1 170 6.1 6.2 7.3 Phenomenonof resin None None None — threading from the peeled surfaces LEGEND:*“LDPE” denotes low-density polyethylene, “HDPE” denotes high-densitypolyethylene, “PP” denotes propylene homopolymer, and “PS” denotespolystyrene.

Examples 13-15 and Comparative Example 5

A double layer film was formed in accordance with the proceduresemployed for Example 10 except that the resin composition used to formthe sealant layer was changed to a composition comprised of 60 weightpercent of PE 1, 15 weight percent of PE 4 and 25 weight percent of PB 1as shown in Table 1.

By way of stacking over the sealant layer side of the obtained doublelayer film each adherend film having a thickness of 200 μm as mentionedin Table 4, heat sealing was executed under the same conditions asadopted for the said heat seal strength test, and then the heat sealstrength was measured. At the same time, the peeled surfaces wereobserved so as to evaluate whether the phenomenon of resin threading hadtaken place from the peeled surfaces. Results of the tests are shownalongside in Table 4.

TABLE 4 Example Example Example Compar. 13 14 15 Example 5 Heat sealstrength LDPE HDPE PP PS (N/15 mm) Sealing temperature 120 (° C.) 4.43.8 — Failed 130 4.6 4.3 6.2 in sealing 140 5.0 5.3 6.7 150 4.8 5.3 6.6160 4.9 5.3 7.0 170 — — 6.8 Phenomenon of resin None None None —threading from the peeled surfaces

As the results set forth in Tables 3 and 4 clearly show, in case theadherend is polyethylene film or polypropylene film, good adhesive wasachieved with the sealant film layer, and its heat seal strength waswithin a feasible range with regard to the easy peel feature. Besides,there was not observed any resin threading phenomenon, and hence suchsealant film was found suited to the packaging application, although itdid not adhere to polystyrene film.

Example 16

A double layer film was prepared by lap jointing a polyester(polyethylene terephalate) film having a thickness of 12 μm to alow-density polyethylene film having a thickness of 25 μm using ananchor coating agent, and then by laminating a sealant film layer overthe surface of the low-density polyethylene film in the double layerfilm employing the extrusion lamination technique, and thus was obtaineda triple film layer wherein the thickness of the sealant film layer was20 μm.

As the resin to constitute the sealant film layer, a resin compositioncomprised of 80 weight percent of PE 5 and 20 weight percent of PB 3mentioned in the Table 1 was used.

Extrusion lamination was executed using a lamination machine having ascrew diameter of 65 mm and equipped with a 500 mm-wide die. Theoperating temperatures for the respective zones in the extruder were setas follows:C1/C2/C3/C4/D=200° C./270° C./305° C./305° C./305° C.The extrusion speed was 80 m/min.

Conditions in which the extrusion lamination was executed were evaluatedand the obtained triple layer film was examined with respect to itsproperties. Results of the examination are set forth in Table 5. Aneck-in characteristics, a draw-down characteristics and the heat sealstrength were determined in accordance with the following procedures.

(1) Neck-in characteristics: After a sealant film was formed underconditions of a film thickness of 20 μm and film take-up speed of 80r/min., neck-in values along the both edges were measured.

(2) Draw-down characteristics: The film take-up speed of the sealantfilm was increased from that set for the time of the neck-incharacteristics test and the take-up speed at which the film was brokenwas recorded as draw-down values.

(3) Heat seal strength: High-pressure process low-density polyethylenefilm having a thickness of 200 μm was stacked as the adherend over thesealant layer side of the obtained triple layer film and heat sealingwas executed under the same conditions as applied in the heat sealstrength test. Thereupon, its heat seal strength was measured. At thesame time, the peeled surfaces were observed so as to evaluate whetheror not the phenomenon of resin threading had developed.

Comparative Example 6

A triple layer film was obtained in accordance with the proceduresemployed for Example 16 except that the resin composition comprised 80weight percent of PE 5 and 20 weight percent of PB 4 for the resin toform the sealant layer film. Conditions in which the extrusionlamination was executed were evaluated and the obtained triple layerfilm was evaluated with respect to its properties. Results of theevaluation are set forth in Table 5.

TABLE 5 Example Compar. 16 Example 6 Resin composition of the sealantlayer (% by weight) PE 5 80 80 PB 3 20 — PB 4 — 20 MFR_(PE)/MFR_(PB) 2.50.5 Conditions of extrusion lamination Resin pressure (kg/m²) 44 38Resin temperature immediately 291 290 below die (° C.) Neck-incharacteristics (mm) 54 58 Draw own characteristics (m/min.) 260 300Fume/smoke emitted from the extruder None None Heat seal strength (N/15mm) Heat seal temperature (° C.) 130 3.4 2.8 140 3.7 3.1 150 4.2 3.6 1605.3 3.7 Phenomenon of resin threading None Yes from the peeled surfaces(Inferior)

As can be seen from the conditions of extrusion lamination of Example 16in Table 5, the resin composition used in Example 16 showed the smallerneck-in value, good draw-down characteristics, and there was notobserved emission of fume/smoke from the extruder which in otherinstances may be caused by degradation of the resin composition theextrusion stage. Since a larger neck-in value represents an increaseddifference in the film thickness between a center portion and both edgeportions and necessitates that much broader trimming area along eachedge of the film in the film production step, a large neck-in value isby no means preferable from the practical point of view. Further, sincethe draw-down characteristic means an index of film productivity, it isdifficult to form film at a high speed when the draw-down characteristicis small.

INDUSTRIAL APPLICABILITY

The sealant resin composition of the present invention gives good filmforming properties, and the film formed therefrom has a practicallysufficient heat seal strength, while an adequate balance is maintainedbetween the heat sealability and the peelability. In light of thefinding that the degree of dependence of the heat seal strength of thefilm on temperature in the heat sealing stage is low, the film is foundto have excellent compatibility with the automatic packaging machine.Furthermore, when the heat sealed surfaces are forcibly peeled apart,there is hardly observed any thread-like resinous residue left on thepeeled surfaces, and hence the film is suitable for the food packagingapplication. Moreover, the film hardly suffers blocking, and there isvirtually no transfer of odor to the packed contents.

By virtue of the features, the sealant film formed from the resincomposition and laminated films and containers, for which the sealantfilm is utilized, are adequate hermetic seal packaging materials havingthe easy peel feature, which all in all particularly suit the foodpackaging application.

1. A sealant resin composition comprising 60 to 95 weight percent of anethylene polymer having a melt flow rate of 0.2 to 30 g/10 min. and adensity of 0.900 to 0.940 g/cm³ and 5 to 40 weight percent of a 1-butenepolymer having a melt flow rate of 0.1 to 25 g/10 min. and a 1-buteneunit content of 60 to 100 mol. percent, wherein a ratio of the melt flowrate (MFR_(PE)) of the ethylene polymer to the melt flow rate (MFR_(PB))of the 1-butene polymer, i.e., MFR_(PE)/MFR_(PB), is not less than 1,wherein the composition has a melt flow rate of 0.2 to 30 g/10 min., anda film formed from the composition has a seal strength of 1 to 10 N/15mm. when the film is heat-sealed at 150° C. and does not substantiallyproduce any thread-like resinous residue when sealed surfaces are peeledapart.
 2. A sealant resin composition according to claim 1, wherein theresin composition comprises an ethylene polymer having a melting pointof a region of 100 to 125° C. as measured by a differential scanningcalorimeter (DSC) and a 1-butene polymer having a melting point of aregion of 70 to 130° C. as measured by the same method.
 3. A sealantresin composition according to claim 1, wherein the resin compositionhas two or more melting peaks in a region of 70 to 130° C. as observedin a DSC measurement.
 4. A sealant resin composition according to claim3, wherein the resin composition has a melting peak having a largestpeak area in a region of 100 to 125° C.
 5. A sealant resin compositionaccording to any one of claims 1 to 4, wherein the resin composition hasa microstructure constituting an islands-in-the-sea structure.
 6. Asealant resin composition comprising 60 to 95 weight percent of anethylene polymer having a melt flow rate of 0.2 to 30 g/10 min. and adensity of 0.900 to 0.940 g/cm³ and 5 to 40 weight percent of a 1-butenepolymer having a melt flow rate of 0.1 to 25 g/10 min. and a 1-buteneunit content of 60 to 100 mol. percent, wherein a ratio of the melt flowrate (MFR_(PE)) of the ethylene polymer to the melt flow rate (MFR_(PB))of the 1-butene polymer, i.e., MFR_(PE)/MFR_(PB), is not less than
 1. 7.A sealant resin composition according to claim 6, wherein the 1-butenepolymer has a density of 0.880 to 0.925 g/cm³.
 8. A sealant resincomposition according to claim 6 or 7, wherein the 1-butene polymer hasa melt flow rate of 2 to 25 g/10 min.
 9. A sealant resin compositionaccording to claim 6 or 7, wherein the 1-butene polymer has a melt flowrate of 2.5 to 25 g/10 min.
 10. A sealant resin composition according toclaim 6, wherein the 1-butene polymer is a 1-butene homopolymer.
 11. Asealant resin composition according to claim 6, wherein the 1-butenepolymer is a copolymer of 1-butene and α-olefin having 2 to 20 carbonatoms except 1-butene.
 12. A sealant resin composition according toclaim 6, wherein the ethylene polymer is a high-pressure processlow-density polyethylene.
 13. A sealant resin composition according toclaim 6, wherein the ethylene polymer is a linear ethylene-α-olefincopolymer of ethylene and α-olefin having 3 to 20 carbon atoms.
 14. Asealant resin composition according to claim 6, wherein the ethylenepolymer is a composition comprising a high-pressure process low-densitypolyethylene and a linear ethylene-α-olefin copolymer.
 15. A sealantresin composition according to claim 14, wherein the ethylene polymer isa composition having a mixing ratio of the high-pressure processlow-density polyethylene to the linear ethylene-α-olefin copolymer setat 0/100 to 75/25 (parts by weight).
 16. A sealant resin compositionaccording to claim 1, wherein the resin composition is a resin usablefor extrusion lamination, cast molding or tubular film process.
 17. Asealant film comprising the sealant resin composition according to claim1 whose thickness is 3 to 100 μm.
 18. A sealant film according to claim17, wherein the film is formed by extrusion lamination, cast molding, ortubular film process.